Question

Threshold frequency for a metal is $10^{15} Hz$. If the light of wavelength $4000 \mathring {A}$ falls on its surface, then which of the following statement is correct?

• A. photoelectrons come out with a velocity of 100 m/sec
• B. no photoelectric emission takes place
• C. photoelectrons come out with a velocity of 124 m/sec
• D. photoelectrons come out with a velocity of 9.8 m/sec.

Answer 1

Answer: (B)

no photoelectric emission takes place

Answer 2

Given: Threshold frequency $\left(f_{0}\right)=10^{15} \,Hz$ and wavelength of light $(\lambda)=4000\,??. We know that threshold wavelength$\left(\lambda_{0}\right)=\frac{c}{f_{0}}=\frac{3 \times 10^{8}}{10^{15}}=3 \times 10^{-7}, m$$=3000 ,??. Since $\lambda>\lambda_{0}$, therefore no photocmission will take place.